This invention relates generally to parking brake actuators and, more particularly, to a parking brake actuator that is continuously self-adjustable for cable slack.
Parking brakes are customarily provided on automotive vehicles to provide a device for securing the vehicle against inadvertent movement when parked on a grade, whether or not the vehicle transmission is engaged or not. Recently, because of space limitations, parking brakes have been developed that utilize a foot-operated flexible cable to operate the remote parking brake. Many of these have a self-adjust feature to accommodate cable slack which occurs during installation or over the life of the vehicle, due to cable stretch or cable system geometry change caused by use.
Such a parking brake is illustrated in U.S. Pat. No. 4,612,823 to De Leeuw et al. This parking brake actuator features a pedal actuator lever that drivingly engages a cable-connected drive plate through a pawl-and-sector connection. Another pawl-and-sector device provides position control to hold the parking brake in applied position and is released to disengage the parking brake.
The driving pawl-and-sector device automatically disengages in brake released position to enable a clock spring to take up slack. The pawl automatically engages the peripheral sector teeth when the pedal lever is depressed to apply the parking brake. This pawl-and-sector driving engagement is subject to the pawl skipping a sector tooth during initial engagement.
This "skip" is inherent in this type of drive, which enables a positive driving engagement between the pedal lever and the drive plate periphery only at spaced intervals determined by sector tooth spacing. The "skip" is caused by the interaction of the pawl and the sector teeth resulting from pawl and tooth geometry, pawl inertia and by the spring rate of the pawl spring. The skipping of a tooth is undesirable if repeatability of the parking brake application action (i.e. effort and motion) is desired.
It would be desirable to provide a self-adjusting parking brake actuator in which the drive clutch comprises a member which continuously engages the periphery of the drive plate.
It would also be desirable to provide a drive clutch which comprises a member that continuously and positively engages the periphery of the drive plate to provide a continuous mechanical driving connection between the operating lever and the drive plate.